The testes produces two classes of C19-steroids, C19O2-androgens and C19O-16-androstenes, from a common precursor, pregnenolone, This project aims to explore the mechanisms that regulate which steroid is formed by investigating the salient characteristics of the enzymatic process that synthesize each steroid. The biosynthesis of 16-androstenes will be studied in order to determine whether oxygenation at C-21 is part of the enzymatic process. The identification of such a 21-oxygenated intermediate, free or enzyme bound, is necessary to determine which enzymes might be targets for a regulatory mechanism. Attempts will be made to identify receptors for the 16-androstenes. Since the function of these unsaturated steroids is at present unknown, clues about their role may be obtained by searching for tissue receptors which presumably would be present in target organs. Finally it may be possible to detect cytoplasmic factors that regulate the formation of androgens and 16-androstenes. A cytoplasmic protein that activates 21-hydroxylase in adrenals has already been detected by us. Attempts will now be made to determine whether similar factors exist for the activation of enzymes involved in the biosynthesis of testicular steroids. These investigations should shed some light on the mechanism(s) that regulate the production of these classes of compound. Since other pairs of steroid hormones are also formed from a single precursor in other microsomes (e.g., androgen and cortexolone in the adrenals or androgen and estrogen in the ovaries), this study can be of significance for our understanding of many important steroidogenic processes.